Protection relays are used in power systems to detect faults or abnormal conditions that could result in equipment damage and/or system instability. When applied correctly, these relays should isolate the faulted circuit only by tripping the appropriate circuit breaker/s, thereby maintaining supply to the rest of the system. Protection relays play a vital role in all industries and should not be overlooked when it comes to commissioning and maintenance testing.
Why is Protection Relay Testing Required?
Testing ensures that the power system or electrical asset, for example a generator or transformer, is appropriately protected. Specifically, testing is done to:
- ensure the protection relay is operating within the tolerances specified by the manufacturer,
- confirm that the appropriate protection settings and logic have been applied as per the latest design and protection study,
- ensure the relay trips the circuit breaker (if possible), and
- identify any concerns that should be addressed.
When should protection relay testing be done?
Following the procurement of the protection relay from the manufacturer, testing should be carried out at several different stages of the electrical installation’s lifecycle. These stages can be defined as:
- Factory acceptance testing – this ensures the protection relay is in good working order after installation into the switchboard/panel and before it is shipped to site. Any defective components or replacements can be ordered at this stage and reduces delays on site.
- Site acceptance testing and commissioning – this ensures the protection relay has not been damaged during transportation and requires full integration with the complete electrical system, for example the circuit breaker, current transformers (CTs) and voltage transformers (VTs). The final protection settings and logic as detailed in the protection study report will also be confirmed and proven at this stage.
- Periodic maintenance testing – this ongoing testing ensures the protection relay is not faulty and operates as expected. The intervals for this testing are usually set by the relay owner and can range from between one (1) to four (4) years depending on the relay’s type, application and environment as well as the manufacturer’s recommendations.
What protection relay tests are required?
The types of tests and inspections required for protection relays can depend on the owner of the equipment, however the following are recommended:
- Physical inspection of the relay hardware, wiring and terminal connections,
- Compare the protection settings with those specified in the latest protection study report,
- Confirm the correct CT and VT ratios have been set in the system configuration and other equipment ratings are correct (if applicable), i.e. apparent power, vector group, line impedance etc.
- Test the pick-up and trip times of each enabled protection element using secondary injection,
- Check the operation of all configured trip and alarm output contacts,
- Test the operation of any user-programmable relay logic,
- Check the operation of configured relay binary inputs,
- Check the operation of the relay’s LED indications (if applicable),
- Check the condition of the relay HMI display and confirm correct annunciation of alarms and trips (if applicable),
- Check the operation of the event and disturbance recorder (if applicable),
- Check the relay has the correct date and time (if applicable),
- Perform a trip test through to the circuit breaker to prove the entire trip circuit (if possible).
Many testing companies can provide you with detailed lists of their services for protection scheme testing.
FINDING a RELIABLE protection relay TESTING COMPANY
Protection relay testing is an important task that, if not performed correctly, can lead to unwanted trips/outages, equipment damage, loss of production or the inadequate protection of electrical assets. It is therefore essential to select a company that has a successful record in delivering on time and without any incidents. The following points should be considered when selecting a relay testing service provider:
- Demonstrated experience and expertise
- State-of-the-art test equipment
- Trained and competent staff
- Good safety culture